1. Field of the Invention
This invention relates to the manufacture of a tire and, more particularly, to an improved tire building apparatus including a novel pneumatic actuator mechanism for radially moving a plurality of drum segments between an expanded, building position wherein the drum is adapted to receive a breaker and a tread portion of the tire for building thereon prior to a vulcanizing process and a collapsed, removal position wherein the drum is removed from the tire thus built.
2. Background
In the manufacture of an automobile tire, such as radial tires, it is common practice to make use of a drum type tire building apparatus such as one having a segmented drum for building a steel belt. This tire building apparatus can be pneumatically or hydraulically operated between an expanded, building position wherein a breaker, a tread and the like are built on the segmented drum and a collapsed, removal position wherein the segmented drum has a reduced diameter to allow its removal from the built tire. The tire building apparatus usually have the capability of varying the diameter of the segmented drum so as to accommodate for various sizes of tires. Some of the apparatus have a single air line through which air is introduced into, and removed from, their pneumatic actuator, and some have a double line system wherein two separate lines are provided for pressurization and depressurization of the pneumatic actuator.
A typical, prior art tire building apparatus having a single port is shown in FIG. 1. It includes a central shaft 10, a sleeve 12 mounted on the shaft, a plurality of drum segments 14 radially movable between an expanded, building position and a collapsed, removal position, a pair of opposed, annular, drum guides 16, return springs 18 for biasing the drum segments toward their removal position, and an annular bladder 20 adapted to move the drum segments 14 to their building position. The upper portion of FIG. 1 depicts, in solid lines, a drum segment 14 held in its expanded, building position by the inflated bladder 20. The lower portion of the figure shows the drum segment 14' diametrically opposite to the segment 14, which has moved to its collapsed, removal position because the deflated bladder allows the return springs 18 to move the drum segment 14' radially inwardly. When it is desired to move the drum segment radially outwardly to the buidling position, the bladder 20 is inflated to the illustrated condition by introducing air through an air passage 22 into the bladder. Conversely, allowing the air to escape from the bladder will cause the drum to collapse due to the action of the return springs.
While suitable bladder devices are commercially available for providing the desired function of varying drum diameter, there are certain limitations inherent in such a bladder type apparatus, as stated below:
(1) It is extremely difficult to uniformly move all the drum segments radially in equal increments because of variations in thickness of bladder material and each segment's resistance to movement, and imbalances of return spring forces.
(2) The bladder is subject to movement or deformation under the influence of other forces than the inside pressure of the bladder, such as stitcher pressures, thus making it rather difficult to produce high quality tires in a stable manner.
(3) Because of a relatively large amount of air required to inflate the bladder, it takes considerable time to move the segmented drum radially between the expanded, building and collapsed, removal positions thus adversely affecting the productivity of a tire manufacturing operation.
(4) Many parts such as a bladder, return springs, etc. are expendable and have to be replaced at periodic intervals or when failed. Since the bladder is surrounded by the segmented drum, a troublesome and time-consuming dismantlement of the drum apparatus will be required if replacement of the bladder is needed.
It is, therefore, an object of the present invention to provide a tire building apparatus that circumvents or minimizes the problems heretofore noted.
It is another object of the invention to provide an improved tire building apparatus including a novel pneumatic actuator mechanism for enabling a uniform and precise radial movement of each drum segment to provide a completely round drum surface for building a tire.
It is a further object of the invention to provide an improved tire building apparatus which employes a stationary piston and a movable cylinder wherein an axial movement of the cylinder is converted to a radial movement of the segmented drum by way of mechanical links.
It is a still further object of the invention to provide an improved tire building apparatus of the segmented drum type that has the capability of varying the diameter of the drum when in its expanded, building position.